The present invention relates to a travel control apparatus for controlling travel of industrial vehicles, such as a forklift.
Forklifts are widely used as a conventional industrial vehicle for load handling operations (load lifting operations and load placing operations) within premises of a factory. It is necessary for a driver to carry out load handling operations in addition to driving the vehicle of this type of forklift, and therefore, the driver sometimes leaves the vehicle in an idling state. Thus, forklifts have recently been put into practical use to which a function has been installed that prevents them from being driven without a driver by detecting that the driver has left the seat and making sure that the forklift is in the neutral state (the state where no drive force is transmitted to the driving wheels even when the accelerator pedal is pressed down) when there is no driver. In the forklift in Japanese Laid-Open Utility Model Publication No. 2-51934, for example, a seat switch for detecting whether a driver is sitting in the driver's seat is provided, and in the case where the seat switch detects that the driver has left the seat, electricity is cut off from the solenoid valve for switching the flow of hydraulic oil to the transmission (clutch mechanism) connected to the engine.
Though Japanese Laid-Open Utility Model Publication No. 2-51934 discloses a forklift having an engine, it is also possible for a battery-driven vehicle, which has a battery and travels by means of the power of the drive motor, to have the same function as that in the above described publication through motor control. As described in Japanese Laid-Open Patent Publication No. 2003-235114, for example, the above described control may include regenerative braking depending on the situation.
Incidentally, the idea of the above described function which is installed in the forklift in Japanese Laid-Open Utility Model Publication No. 2-51934 and prevents it from being driven without a driver was thought of under the premise that the vehicle is in a stopped state. Therefore, in the case where the driver leaves the seat when the forklift is in a stopped state, the forklift can be prevented from moving because the forklift remains in the neutral state even when the direction lever (for making the vehicle travel forward or backward at the driver's will) is mistakenly operated in the state where the driver has left the seat. In the case where the driver leaves the seat when the forklift is in a traveling state, however, the forklift travels in the neutral state. The vehicle in this state naturally reduces speed, and therefore, the stopping distance becomes long. Thus, in the case of a battery-driven vehicle, it is possible to use the regenerative brakes disclosed in Japanese Laid-Open Patent Publication No. 2003-235114 so that the regenerative brakes make the stopping distance short even in the case where the driver leaves the seat when the forklift is in a traveling state.
Forklifts, however, have a great difference in the stability of the vehicle when traveling depending on the loading state, as can be seen from its characteristics in terms of the application. For example, the location of the center of gravity of the vehicle changes between the state of carrying a load and the state of carrying no load, and therefore, there is a difference in the stability of the vehicle when traveling. In the state of carrying a load, there is also a difference in the stability of the vehicle when traveling depending on the weight of the load (load weight), the height of the fork, the tilt angle of the fork and the like. Therefore, in the case where the driver leaves the seat of a forklift having regenerative brakes when a load is placed on the fork, for example, in a state where the fork is raised high, the regenerative brakes are applied as the driver leaves, and thus, there is a risk that the stability of the vehicle when traveling may be reduced.